"We sort of already know who's served there because we could always look at the service records -- but it was not as easy as it is now."
He said the digitisation of records by Archives New Zealand had made the cross referencing a lot easier than it would have been in earlier days, when hard copies had to be tracked down.
"The original figure of 8556 was given by Sir Ian Hamilton, who was the commander of the entire expedition. His staff had calculated that figure but it was never really challenged at the time."
Mr Francis said that number became the official history, but military historians like Christopher Pugsley and Richard Stowers had come to the conclusion the original figures must have been miscalculated.
The new research carried out was "really just trying to get a better grasp on history".
He said a lot of men left Gallipoli wounded or sick, were taken to hospital, and then returned after recovery.
"So there were a lot of men coming and going and it was hard to keep track.
"Some men went to Gallipoli three times, some possibly more than that."
Mr Francis suspected the new figure of people posted to the Gallipoli campaign was "probably still conservative" and it could be more like 17,000 soldiers who served.
He said the figure had not included anyone who landed in Gallipoli from the seventh reinforcement. However, at least one man went -- Wairarapa doctor, Norman Price.
"There will probably only be a small number, but if Norman went there will probably be a number of others."
Mr Francis said there could be more men from Wairarapa who served in the campaign than was now known. "Every now and then we get records that are so brief we don't actually know whether they were there. The ones who served early in the war, their records are in no way as in-depth as the men's who served later in the war. And the men we have tended to know a lot more about are the ones who died there."
